1. C# 4.0 and .NET 4.0 Buu Nguyen, MVP (ASP.NET) www.buunguyen.net/blog buunguyen@kms-technology.com Microsoft Confidential 1

2. Agenda Optional and Named Parameters Covariance and Contravariance Dynamic Binding Threading with Task API Task Parallel Library (TPL) PLINQ

3. Optional and Named Parameters

4. ?Quiz What are 2 issues of this API?

5. Covariance and Contravariance

6. ?Quiz What is wrong with this code?

7. Covariance Defined Let’s say S is subtype of B and GT is a generic type GT<S> behaves like subtype of GT<B> on assignment compatibility, i.e. GT<S> s = … GT<B> b = s; GT<S> s = (GT<S>)b; Safe only when GT doesn’t expose members “receiving” T as input (aka input-safe) Microsoft Confidential 7

8. ?Quiz What is wrong with this code?

9. Contravariance Defined Let’s say S is subtype of B and GT is a generic type GT<B> behaves like subtype of GT<S> on assignment compatibility, i.e. GT<B> b = … GT<S> s = b; GT<B> b = (GT<B>)s; Safe only when GT doesn’t expose members “returning” T as output (aka output-safe) Microsoft Confidential 9

10. Dynamic Binding

11. ?Quiz Write a method that prints out the Name property of an anonymous object returned by another method

12. Dynamic binding means… use runtime type for all bindings

13. ?Quiz A method summing Length properties of all parameters, regardless of actual type

14. ?Quiz How to builds C# objects that behave like JavaScript objects, i.e. members can be added at any time?

15. ?Quiz Write a class whose objects can invoke static methods of any particular type Bonus #1: include non-public static methods Bonus #2: ignore case

16. ?Quiz Write a class whose objects can be used as result-caching proxy for the method invocation of any other object

17. Task Parallel Library (TPL) & PLINQ

18. ?Quiz Write a method calculating Fibonacci number using a thread in thread-pool and returning result to caller

19. Task Parallelism Features Wait on tasks Support parent-child relationship Exception handling Cancelling tasks Continuation Execute one task after another Microsoft Confidential 19

20. ?Quiz Write 3 methods: Calculate some known Fibonacci numbers Calculate Fibonacci numbers for a range Calculate Fibonacci numbers for a list of specified indexes Each calculation must take place in a thread in thread-pool

21. Parallel Class Assign delegates to a handful of Task instances, not one-to-one mapping

22. ?Quiz Write a method which calculate some specified Fibonacci numbers and return the sum of them to the caller